Scan-type radar apparatus for a vehicle to accurately detect an object in a lane of the radar equipped vehicle

ABSTRACT

A scan-type radar apparatus for a vehicle which determines whether an object detected by the radar exists in the lane in which the radar equipped vehicle is moving with a high accuracy while restricting an increase of the manufacturing cost of the radar apparatus. A scan-type radar detects objects existing in a detectable range, the scan-type radar apparatus assuming a vehicle moving lane area corresponding to a vehicle moving lane in which the vehicle is moving based on an operating condition of the vehicle, the vehicle moving lane area being assumed within the detectable range. An actual direction of each of the objects is detected by the scan-type radar with respect to the radar equipped vehicle. A delay direction is calculated when the actual direction detected by an object direction detecting arrangement is changed with respect to time, the delay direction indicating a direction of a virtual position of each object with respect to the vehicle by being provided with a predetermined time delay with respect to a change in the actual direction. It is determined whether each object exists within the vehicle moving lane based on the delay direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a scan-type radar provided on a vehicleand, more particularly, to a scan-type radar apparatus which detects anobject existing in a lane in which the radar equipped vehicle is moving.

2. Description of the Related Art

Conventionally, a radar apparatus for a vehicle which detects an objectanterior to the radar equipped vehicle is known, for example, inJapanese Laid-open Patent Application No.6-150195. This conventionalradar apparatus comprises a radar which is capable of detecting thepositions and orientations of a plurality of objects existing in a widearea anterior to the radar equipped vehicle. According to such a radarapparatus, a relative position of each of the objects existing in thedetectable range with respect to the radar equipped vehicle can bedetected.

In order to utilize the results of the radar apparatus for the controlof a vehicle operation, it is required to accurately determine whetherthe objects detected by the radar apparatus exist in the lane in whichthe radar equipped vehicle is moving. Hereinafter, the lane in which theradar equipped vehicle is moving may be referred to as a radar equippedvehicle moving lane. When the radar equipped vehicle is moving in astraight line, it can be assumed that the radar equipped vehicle movinglane extends forwardly of the radar equipped vehicle and has apredetermined lane width. Accordingly, in such a case, an areacorresponding to the radar equipped vehicle moving lane can beaccurately recognized within the detectable range of the radarapparatus. When the radar equipped vehicle moves along a curve, it canbe assumed that the radar equipped vehicle moving lane extends forwardlyof the radar equipped vehicle in accordance with the radius of curvatureof the curve. Accordingly, if the radius of curvature is known, the areacorresponding to the radar equipped vehicle moving lane can berecognized in the detectable range of the radar apparatus.

In the above-mentioned conventional radar apparatus having a widedetectable range in the anterior of the radar equipped vehicle, anobject existing in the radar equipped vehicle moving lane can bedetected in the detectable range whether the radar equipped vehicle ismoving on a straight road or a curved road. The radius of curvature of aroad on which the radar equipped vehicle is moving can be assumed basedon an operating condition of the vehicle such as a yaw rate w_(y).Accordingly, in the above-mentioned conventional apparatus, a lane areaof the radar equipped vehicle can be recognized in response to theoperating condition of the vehicle. Thus, an object which is not in theradar equipped vehicle moving lane can be distinguished from an objectin the radar equipped vehicle moving lane, when the object is detectedby the radar apparatus, by determining whether or not the object is inthe recognized lane area.

If an object detected by the radar apparatus is a vehicle movinganterior to the radar equipped vehicle, the object vehicle enters acurve before the radar equipped vehicle enters the curve. Accordingly,in the method in which the lane area is determined by assuming theradius of curvature based on the operating condition, an object in theradar equipped vehicle moving lane may be erroneously recognized as onewhich is not in the radar equipped vehicle moving lane during the periodfrom the time when the object, such as a vehicle moving anterior to theradar equipped vehicle, enters a curve to the time when the radarequipped vehicle enters the curve.

The above-mentioned problem may be eliminated by setting a lane areahaving a greater width in the detectable range. Alternatively, theproblem can be eliminated by detecting the radius of curvature of theroad extending in an anterior direction of the radar equipped vehicle byusing an image recognizing apparatus. However, the former method maydecrease the accuracy of discrimination between objects existing and notexisting in the radar equipped vehicle moving lane. The later method mayincrease manufacturing cost of the radar apparatus. As mentioned above,in the conventional radar apparatus, it is difficult to provide a radardetection function which accurately discriminate between an objectexisting in the radar equipped vehicle moving lane and an object whichis not existent in the radar equipped vehicle moving lane, at a lowmanufacturing cost.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedand useful radar apparatus for a vehicle in which the above-mentionedproblems are eliminated.

A more specific object of the present invention is to provide ascan-type radar apparatus for a vehicle which determines, with highaccuracy, whether an object detected by the radar exists in the lane inwhich the radar equipped vehicle is moving while restricting an increaseof the manufacturing cost of the radar apparatus.

In order to achieve the above-mentioned object, there is providedaccording to the present invention a scan-type radar apparatus providedon a vehicle, comprising:

a scan-type radar for detecting objects existing in a detectable range,the scan-type radar apparatus assuming a vehicle moving lane areacorresponding to a vehicle moving lane in which the vehicle is movingbased on an operating condition of the vehicle, the vehicle moving lanearea being assumed within the detectable range;

object direction detecting means for detecting an actual direction ofeach of the objects detected by the scan-type radar with respect to thevehicle;

delay direction calculating means for calculating a delay direction whenthe actual direction detected by the object direction detecting means ischanged with respect to time, the delay direction indicating a directionof a virtual position of each of the objects with respect to the vehicleby being provided with a predetermined time delay with respect to achange in the actual direction; and

existence determining means for determining whether each object existswithin the vehicle moving lane based on the delay direction.

According to the above-mentioned invention, the scan-type radar detectsthe object existing in the detectable range to generate datacorresponding to each of the objects. The direction of each of theobject is calculated based on the data generated by the scan-type radar.The direction of an object detected by the radar is shifted in atransverse direction when the object enters into or exits from a curveprior to the radar equipped vehicle. When such shift occurs, the delaydirection is calculated which is provided with the predetermined timedelay. The delay direction is shifted slower than the actual directionof the object due to the time delay being provided thereto. Thus, thevirtual position of the vehicle indicated by the delay direction remainswithin the vehicle moving lane area immediately after the object entersor exits a curve. After the radar equipped vehicle following the objectenters or exits the curve, the vehicle moving lane area assumed by theradar apparatus is corrected to an appropriate area in which the objectactually exists. Thus, the position of the object indicated by the delaydirection always exists within the assumed vehicle moving lane area.

In the present invention, the delay direction calculating means maycomprise a blunted value calculating means for calculating a bluntedvalue of the actual direction as the delay direction. In one embodimentof the present invention, the blunted value is obtained from the actualdirection being processed by a digital filtering method. The bluntedvalue shows a relatively gentle and smooth change as compared to thedelay direction directly obtained from the actual direction. Thus, anaccurate determination can be performed when a radius of curvature of aroad fluctuates. Additionally, a chattering generated in the control ofthe radar apparatus due to small fluctuations of the direction can beprevented.

The scan-type radar apparatus according to the present invention mayfurther comprise change rate detecting means for detecting a change rateof the actual direction of each of the objects, wherein the existencedetermining means comprises lane width changing means for decreasing awidth of the vehicle moving lane area when the change rate exceeds apredetermined value.

According to this invention, the change rate is detected when thedirection of the object is shifted. The change rate of the directionwhen the object enters into or exits form a curve is smaller that thechange rate when the object moves from the vehicle moving lane toanother lane. Thus, an object changing a lane can be immediatelyexcluded from the objects determined to be existent in the vehiclemoving lane by decreasing the width of the vehicle moving lane.

Additionally, in the scan-type radar apparatus according to the presentinvention, the delay direction calculating means may comprise delayamount setting means for providing the predetermined time delay to eachof the objects detected by the scan-type radar.

In this invention, if the predetermined time delay is set to a largevalue, that is, if the amount of delay of the delay direction withrespect to the actual direction of the object is large, the possibilityof an erroneous determination that the object in the vehicle moving laneis determined as an object existing in other lanes is decreased.

Additionally, the scan-type radar apparatus according to the presentinvention may further comprise correspondence determining means fordetermining whether the change in the actual direction of each of theobjects corresponds to each other, wherein the existence determiningmeans comprises determination maintaining means for determining that oneof the objects continuously exists in the vehicle moving lane when ashift in the actual direction of the one of the objects which has beendetermined to exist in the vehicle moving lane corresponds to a shift inthe actual direction of at least another one of the objects.

When a plurality of objects ahead of the radar equipped vehicle entersor exits a curve, the positions of the objects show similar movementwith respect to the radar equipped vehicle. That is, when the shift inthe directions of the objects correspond to each other, it is determinedthat the objects entered into or exited from a curve prior to the radarequipped vehicle. Thus, in this invention, if the shift in the directionof one of the objects, existing in the vehicle moving lane, correspondsto the shift in the direction of other objects, the one of the objectsis determined to be continuously existing in the vehicle moving lane.

Additionally, in the scan-type radar apparatus according to the presentinvention, the correspondence determining means comprises timedifference assuming means for assuming a time difference between a starttime of a shift in the direction of the objects based on each distancebetween the objects.

When a plurality of objects enter into or exit from a curve, a shift inthe direction of the most remote object is detected first. The starttime of the shift in the direction of each object is detectedsequentially when each object enters into or exits from a curve.Accordingly, there are time differences between the times when the shiftof the direction of each object is detected. Thus, if the shift in thedirection of each of a plurality of objects is detected with timedifferences corresponding to the distances between the objects, it isdetermined that the objects entered into or exited from a curve. In thisinvention, the correspondence of movement of a plurality of objects isdetermined by considering such time differences.

Additionally, the scan-type radar apparatus according to the presentinvention further comprise excluding means for excluding a shortdistance object from the objects determined to exist in said vehiclemoving lane when a shift in the actual direction of the short distanceobject has a change rate greater than a predetermined value for apredetermined time period, the short distance object being one of theobjects positioned within a predetermined short distance from thevehicle in the vehicle moving lane.

In this invention, the short distance object whose direction iscontinuously subjected to large shift for the predetermined time periodis excluded from the objects determined to exist in the vehicle movinglane. Accordingly, the short distance object is not subjected to thedetermination based on the delay direction, and is immediately excludedfrom the objects determined to exist in the vehicle moving lane.

Additionally, the scan-type radar apparatus according to the presentinvention further comprises recognizing means for recognizing a longdistance object as an object existing in the vehicle moving lane duringa first predetermined time period, after a change has occurred in theactual direction of the long distance object with a continuous changerate of more than a predetermined value for a second predetermined timeperiod, the long distance object being positioned beyond a predeterminedlong distance from the vehicle.

When the direction of the long distance object shows a large shift for apredetermined time period, it is determined that the long distanceobject entered or exited a curve or changed a lane. It takes arelatively long time for the radar equipped vehicle to enter or exit thecurve after the long distance object entered or exited the curve. Thus,unlike the short distance object or the middle distance object, thedelay direction of the long distance object which is determined to existin the vehicle moving lane may be shifted out of the vehicle moving lanearea. This results in the exclusion of the long distance object from theobject determined to exist in the vehicle moving lane. However, in thisinvention, the long distance object is not subjected to thedetermination based on the delay direction, and the long distance objectis continuously determined to exist in the vehicle moving lane for apredetermined time period after the shift in the direction of the longdistance object was detected. If the shift in the direction is caused bya change of lane, the delay direction will not return to the vehiclemoving lane. Thus, the long distance object is excluded from the objectsdetermined to exist in the vehicle moving lane at that time. If theshift in the direction is caused by the curve, the delay direction willreturn to the vehicle moving lane area within the predetermined timeperiod. In this case, the long distance object is appropriatelyrecognized as the object which is existent in the vehicle moving lane.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a scan-type radar apparatus for a vehicleaccording to a first embodiment of the present invention;

FIG. 2 is an illustration of a scanning area of the radar apparatusshown in FIG. 1;

FIG. 3 is an illustration of sets of data with respect to objects(targets) detected by a radar ECU shown in FIG. 1;

FIG. 4 is an illustration of an object and a radar equipped vehiclemoving in the same lane;

FIG. 5 is an illustration of a state where the object and the vehicleare in the same curved lane;

FIG. 6 is a flowchart of a control routine performed by a radar ECUshown in FIG. 1;

FIG. 7A is a graph showing a variation of an actual center angleθ_(cent) r when an object and a radar equipped vehicle enters a curve;

FIG. 7B is a graph showing a variation of a delay direction θ_(cent)FILT corresponding to the variation of the actual center angle θ_(cent)r shown in FIG. 7A;

FIG. 8 is an illustration for explaining a relationship between theactual center angle θ_(cent) r and the delay direction θ_(cent) FILTwhen the object enters a curve;

FIG. 9 is an illustration for explaining a relationship between theactual center angle θ_(cent) r and the delay direction θ_(cent) FILTestablished when both the object and the radar equipped vehicle are inthe same curve;

FIG. 10 is an illustration for explaining a relationship between theactual center angle θ_(cent) r and the delay direction θ_(cent) FILTestablished immediately after the object exits the curve;

FIG. 11 is a control routine performed by the radar ECU of a radarapparatus according to a second embodiment of the present invention.

FIG. 12 is an illustration of a radar equipped vehicle and an objectwhich moves to another lane at a time t1 and returns to the radarequipped vehicle lane at a time t2;

FIG. 13A is a graph showing a variation of the actual center angleθ_(cent) r;

FIG. 13B is a graph showing a variation of the delay direction θ_(cent)FILT corresponding to the variation of the actual center angle θ_(cent)r shown in FIG. 13A;

FIG. 14 is a control routine performed by the radar ECU of a radarapparatus according to a third embodiment of the present invention;

FIG. 15A is a graph, similar to FIG. 13A, a variation of the actualcenter angle θ_(cent) r;

FIG. 15B is a graph showing a variation of a determination value usedfor determining an establishment of a vehicle moving lane condition;

FIG. 16 is an illustration of a radar equipped vehicle and a pluralityof objects including an object existing in the radar equipped vehiclelane and objects moving in other lanes;

FIG. 17 is a graph showing a variation of the actual center angleθ_(cent) r detected by the radar equipped vehicle;

FIGS. 18, 19 and 20 are parts of a control routine performed by theradar ECU of a radar apparatus according to a fourth embodiment of thepresent invention;

FIG. 21 is a graph showing variations of the actual center anglesθ_(cent) r of a short distance object and a long distance object;

FIGS. 22 and 23 are parts of a control routine performed by the radarECU of a radar apparatus according to a fifth embodiment of the presentinvention; and

FIGS. 24 and 25 are parts of a control routine performed by the radarECU of a radar apparatus according to a sixth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of a first embodiment of the presentinvention. FIG. 1 is a block diagram of a scan-type radar apparatus (maybe referred to as simply a radar apparatus) for a vehicle according tothe first embodiment of the present invention. The radar apparatusaccording to the first embodiment of the present invention is controlledby an electronic control unit 30 (hereinafter referred to as a radar ECU30) for controlling the radar and an electronic control unit 32(hereinafter referred to as a environment recognizing ECU 32) forcontrolling vehicle speed by recognizing an operating environment of avehicle.

The radar ECU 30 is connected with a steering angle sensor 34, a yawrate sensor 36 and a vehicle speed sensor 38. The steering angle sensor34 generates a signal (steering angle signal θ_(H)) corresponding to thesteering angle of a steering wheel. The yaw rate sensor 36 generates asignal (yaw rate signal w_(y)) corresponding to the angular velocity ofthe vehicle with respect to the center of gravity thereof. The vehiclespeed sensor 38 generates a pulse signal (vehicle speed signal V) havinga pulse period which varies in response to vehicle speed.

The radar ECU 30 assumes a turning radius R of the vehicle based on thesteering angle signal θ_(H), the yaw rate signal w_(y) and the vehiclespeed signal V. The turning radius R can be calculated based on one ofthe steering angle signal θ_(H) and the yaw rate signal w_(y). Thus,both the steering angle sensor 34 and the yaw rate sensor 36 are notneeded as the turning radius can be calculated by using one of thesensors.

The radar ECU 30 is connected with a radar antenna 40 and a scancontroller 42. The radar antenna 40 is provided adjacent to the frontgrille of the vehicle and is pivotable with respect to a pivot axisextending in a vertical direction. The radar antenna 40 has adirectivity to transmit and receive a signal with a predetermined beamspreading angle.

The radar antenna 40 is coupled to a scan mechanism 44 which swings theradar antenna 40. The scan mechanism 44 is feedback controlled by thescan controller 42. A scan angle signal is supplied to the scancontroller 42 from the radar ECU 30. The scan controller 42 feedbackcontrols the scan mechanism 44 so that the scan angle of the radarantenna 40 corresponds to a designating angle θ_(S) supplied by theradar ECU 30. The radar ECU 30 varies the designating angle θ_(S) at apredetermined period so that the detectable range anterior to thevehicle is scanned by the radar antenna 40.

The radar ECU 30 constitutes, together with the radar antenna 40, aknown Frequency Modulation-Continuous Wave radar (FM-CW radar). That is,the radar ECU 30 controls the radar antenna 40 to transmit apredetermined transmission wave therefrom. The ECU 30 detects data of arelative distance RD and a relative velocity RV with respect to anobject existing anterior to the radar equipped vehicle in a direction ofdesignating angle (scan angle θ_(S)) based on a reflection wave receivedby the radar antenna 40. The radar ECU 30 detects a state of the objectin the detectable range based on the data, and sends the result ofdetection to the environment recognition ECU 32.

The environment recognizing ECU 32 is connected with an alarm 46, abrake 48 and a throttle 50. The environment recognizing ECU 32 controlsthe alarm 46 and a brake 48 or throttle 50 to decelerate the vehicle anddraw the driver's attention, when an object anterior to the vehicle getsclose to the vehicle, in accordance with a predetermined logic.

FIG. 2 is an illustration of a scanning area of the radar apparatusaccording to the present embodiment. In FIG. 2, a vehicle 52 is equippedwith the radar apparatus having the radar 40 shown in FIG. 1. In thepresent embodiment, the scanning area of the radar 40, which correspondsto the detectable range for an object, is a range extending anterior tothe vehicle 52 at an angle of 10 degrees with respect to thelongitudinal axis of the vehicle 52 to both the left and right side ofthe vehicle 52. Hereinafter, the area on the left side is assumed to bean area with a negative scan angle θ_(S), and the area on the right sideis assumed to be an area with a positive scan angle θ_(S).

In the present embodiment, the radar antenna 40 is controlled to scanfrom -10 degrees to +10 degrees for every 100 msec. Additionally, theradar ECU 30 detects data of an object for each 0.5 degrees of the scanangle θ_(S) when the radar antenna 40 scans the area shown in FIG. 2.That is, in the present embodiment, the detectable range is divided into40 areas with 0.5 degrees interval. Thus, 40 sets of data is obtainedwhen the radar antenna 40 scans the detectable range between -10 degreesand +10 degrees of the scan angle θ_(S).

FIG. 3 is an illustration of sets of data with respect to objects(targets) detected by the radar ECU 30. The sets of data in FIG. 3indicate the corresponding scan angle θ_(S) and the relative distancebetween each of the objects and the radar equipped vehicle 52. In FIG.2, there are three targets Tg1 to Tg3. The target Tg1 is detected at anangular position corresponding to the scan angle θ_(S) ranging from -8degrees to -6 degrees. The target Tg2 is detected at an angular positioncorresponding to the scan angle θ_(S) ranging from -1.5 degrees to +1degree. The target Tg3 is detected at an angular position correspondingto the scan angle θ_(S) ranging from +5 degrees to +7.5 degrees.

In the radar apparatus according to the present embodiment, the alarm46, the brake 48 and the throttle 50 must be operated when an object ispositioned close to the vehicle 52 in the lane (hereinafter referred toas a vehicle moving lane) in which the vehicle 52 is moving. In order toachieve such a function, it must be determined whether or not an objectis in the vehicle moving lane based on the sets of data of the objectsas shown in FIG. 3. Additionally, when it is determined that an objectis in the vehicle moving lane, the alarm 46, the brake 48 and thethrottle 50 must be controlled based on the relative distance RD and therelative velocity RV of the vehicle in the vehicle moving lane.

In the present embodiment, after the distribution of the objects asshown in FIG. 3 is obtained, sets of data indicating an angular positionclose to each other are grouped, each of the groups of sets of dataindicates a single object. Then, the center angle of the scan anglescorresponding to each of the grouped sets of data is calculated for eachof the grouped sets of data. Hereinafter, the center angle of each groupof sets of data is referred to as an actual center angle θ_(cent) r. Itis determined whether or not an object is in the vehicle moving lanebased on the determination as to whether or not the actual center angleθ_(cent) r is positioned within the vehicle moving lane.

FIG. 4 is an illustration of an object 54 and the vehicle 52 moving inthe same lane. The object 54, which is, for example, a vehicle anteriorto the radar equipped vehicle 52, is spaced from the radar equippedvehicle 52 with a distance L. The longitudinal axis of the object 54aligns with the longitudinal axis of the vehicle 52. In the state shownin FIG. 4, the range of the scan angle θ_(S) at which the anteriorobject 54 is irradiated by the radar beam of the radar antenna 40 can berepresented by the following relationship (1), where W is a width of theobject 54.

    -tan.sup.-1 (W/2L)≦θ.sub.S ≦tan.sup.-1 (W/2L)(1)

The above relationship (1) can be represented by the followingrelationship (2), where θ_(VH) is an irradiatable scan anglecorresponding to the term "tan⁻¹ (W/2L)" of the relationship.

    -θ.sub.VH ≦θ.sub.S ≦θ.sub.VH(2)

If all of the sets of data with respect to the object 54 are obtainedproperly, the actual center angle θ_(cent) r becomes zero degrees.However, in a practical condition, the actual center angle θ_(cent) rdoes not always become zero degrees. That is, the actual center angleθ_(cent) r can possibly vary within the range from -θ_(VH) to θ_(VH).

The object 54, which is a vehicle moving anterior to the vehicle 52, maymove leftwardly or rightwardly within the width of the vehicle movinglane. Considering such movement, the actual center angle θ_(cent) r canpossibly vary within a range slightly wider than the range from -θ_(VH)to θ_(VH). Accordingly, in the present embodiment, it is determined thatthe object 54 and the radar equipped vehicle 52 are in the same lane ina straight road when the following relationship (3) is satisfied, whereK is a correction factor. In the present embodiment, the correctionfactor K is set to 1.1 (K=1.1).

    -K·θ.sub.VH ≦θ.sub.cent r≦K·θ.sub.VH                        (3)

FIG. 5 is an illustration of a state where the object 54 and the vehicle52 are in the same curved lane having a radius of curvature R and thedistance between the object 54 and the vehicle 52 is maintained at thedistance L. When the object 54 and the radar equipped vehicle 52 aremoving in the curve, a direction θ_(CV) of the object 54 with respect tothe vehicle 52 varies in response to the radius of curvature R. In thiscase, as shown in FIG. 5, the direction θ_(CV), which is an anglebetween the longitudinal axis of the vehicle 52 and a line connectingthe object 54 and the vehicle 52, can be represented as θ_(CV) =sin⁻¹(L/2R). Accordingly, under such a condition, the actual center angleθ_(cent) r of the object 54 moving in the same lane varies from theactual center angle θ_(CV) of a straight lane toward the center of thecurve by the angle θ_(CV). In this case, it is assumed that the object54 is in the same lane if the following relationship (4) is satisfied.

    θ.sub.CV -K·θ.sub.VH <θ.sub.cent r<θ.sub.CV +K·θ.sub.VH               (4)

A straight road is considered to be a curve having an infinite radius ofcurvature. In this sense, it can be determined whether or not the radarequipped vehicle 52 and the object 54 are in the same lane based on theabove-mentioned relationship (4) when the object 52 and the vehicle 54are moving in a curve as well as in a straight lane.

The radius of curvature R of the road on which the object 54 is movingcan be assumed to be equal to the turning radius of the vehicle 52. Inthe present embodiment, as mentioned above, the radar ECU 30 functionsto detect the turning radius Rt of the vehicle 52. Thus, therelationship (4) can be established based on the turning radius Rtcalculated by the radar ECU 30 so as to determined whether the detectedactual center angle θ_(cent) r satisfies the relationship (4). In thismanner, it can be determined with high accuracy whether the object 54and the vehicle 52 are moving in the same lane when both the object 54and the vehicle 52 are on a straight road and also when they are on acurved road.

However, according to the above-mentioned manner, the turning radius Rtof the radar equipped vehicle 52 is assumed to be infinite while theradius of curvature R of the lane between the object 54 and the vehicle52 is varied during the period from the time when the object 54 enters acurve to the time when the radar equipped vehicle 52 enters the curve.Additionally, the turning radius Rt of the radar equipped vehicle 52 ismaintained to be the radius of curvature R of the curve while the radiusof curvature R of the lane between the object 54 and the vehicle 52 isvaried toward an infinite radius during the period from the time whenthe object 54 exits a curve to the time when the radar equipped vehicle52 exits the curve.

When the radius of curvature of the lane between the object 54 and thevehicle 52 does not accurately match the turning radius Rt calculated inthe radar equipped vehicle 52, the condition which is satisfied by theactual center angle θ_(cent) r differs from the condition where theabove-mentioned relationship (4) is satisfied. Thus, there is apossibility that the object 52 in the lane of the vehicle 52 iserroneously determined to be an object which is not in the lane of theradar equipped vehicle 52.

In the present embodiment, an object in the radar equipped vehiclemoving lane is accurately discriminated from objects which are not inthe radar equipped vehicle moving lane without having theabove-mentioned erroneous determination at the time when the radarequipped vehicle enters or exits a curve. FIG. 6 is a flowchart of acontrol routine performed by the radar ECU 30 to achieve theabove-mentioned feature of the present embodiment. The routine shown inFIG. 6 is started every time the scanning operation is performed by theradar antenna 40 from -10 degrees to +10 degrees of the scan angleθ_(S), that is, the routine is started for each 100 msec.

When the routine shown in FIG. 6 is started, the data with respect toobjects detected by the scanning of the radar antenna 40 is processed instep 100. In this step, sets of data each of which are supposed to bederived from a single object is grouped from among all sets of data.Additionally, the relative distance and the relative velocity of each ofthe objects recognized by the grouping of the data are calculated. Then,in step 101, the actual center angle θ_(cent) r of each of therecognized objects is calculated based on the grouped sets of data.

In step 102, it is determined whether or not the object detected at thistime was detected in the previous time. It should be noted that when aplurality of objects are detected at this time, the determination ismade for each of the objects. As a result, it is determined that theobjects for which no corresponding data exists in the previous data isdetermined to be a new object which has entered in the detectable rangeof the radar. The actual center angle θ_(cent) r of the objectdetermined as the object in the detectable range is stored as the centerangle of the object in step 103. Then, the routine proceeds to step 106.

More specifically, if it is determined, in step 102, that the object wasdetected in the previous scanning cycle, the routine proceeds to step104. In step 104, a blunted value θ_(cent) FILT is calculated withrespect to the actual central angle θ_(cent) r. The normalized valueθ_(cent) FILT is calculated by substituting the three most recent actualcenter angle θ_(cent) r (θ_(cent) r(n), θ_(cent) r(n-1) and θ_(cent)r(n-2)) and the two most recent delay directions θ_(cent) FILT (θ_(cent)FILT(n-1) and θ_(cent) FILT(n-2) into the following expression (5).##EQU1##

The above-mentioned expression (5) is a calculation formula for forminga digital low-pass filter. In the expression (5), the constants k1 to k5are provided for determining the cut-off frequency of a filter. In thisembodiment, values of the constants k1 to k5 are set so that the cut-offfrequency becomes 0.25 Hz.

After the process of step 104 is completed, the routine proceeds to step105. In step 105, the delay direction θ_(cent) FILT is stored as anobject center angle θ_(cent), and the routine proceeds to step 106.

FIG. 7A is a graph showing a variation of the actual center angleθ_(cent) r when an object moving in the radar equipped vehicle movinglane enters a curve at time t1 and then the radar equipped vehicle 52enters the curve at time t2. As shown in FIG. 7A, the actual centerangle θ_(cent) r is maintained constant until the time t1 is reached.The actual center angle θ_(cent) r is varied from the time t1 to thetime t2. Then, after the time t1 is passed, the actual center angleθ_(cent) r is maintained to be close to the angle θ_(CV) which isdetermined by the radius of curvature R of the curve and the distancebetween the object and the radar equipped vehicle.

FIG. 7B is a graph showing a variation of the delay direction θ_(cent)FILT corresponding to the variation of the actual center angle θ_(cent)r shown in FIG. 7A. As shown in FIG. 7B, the variation of the delaydirection θ_(cent) FILT is gentle and smooth as compared to thevariation of the actual center angle θ_(cent) r, and varies to followthe actual center angle θ_(cent) r from the time t1 with a slight delaywith respect to the variation of the actual center angle θ_(cent) r.

FIG. 8 is an illustration for explaining a relationship between theactual center angle θ_(cent) r and the delay direction θ_(cent) FILTestablished during a period from the time t1 to the time t2. In FIG. 8,a vehicle moving lane area indicated by the reference numeral (4)corresponds to the vehicle moving lane recognized by the radar equippedvehicle 52. As discussed above, the delay direction θ_(cent) FILT variesslightly later than the variation of the actual center angle θ_(cent) r.Thus, when the object 54 indicated by the actual center angle θ_(cent) rexits the vehicle moving lane due to the object entering a curve, thedelay direction θ_(cent) FILT still remains in the range of the vehiclemoving lane.

FIG. 9 is an illustration for explaining a relationship between theactual center angle θ_(cent) r and the delay direction θ_(cent) FILTestablished after the time t2 and until the object 54 exits the curve.That is, the relationship shown in FIG. 9 is established when both theobject 54 and the radar equipped vehicle 52 are moving in the samecurve. After the time t1, the delay direction θ_(cent) FILT is graduallyvaried toward a direction in which the difference between the actualcenter angle θ_(cent) r and the delay direction θ_(cent) FILT isdecreased. On the other hand, the vehicle moving lane area (4) isshifted toward the turning direction of the vehicle 52 due to theturning motion of the vehicle 52 after the vehicle 52 enters the curve.As a result, the delay direction θ_(cent) FILT remains in the vehiclemoving lane area (4) recognized by the radar equipped vehicle 52.

FIG. 10 is an illustration for explaining a relationship between theactual center angle θ_(cent) r and the delay direction θ_(cent) FILTestablished immediately after the object 54 exits the curve. After theobjects reached the exit of the curve, the actual center angle θ_(cent)r is decreased, and will be shifted out of the vehicle moving lane area(4). However, the delay direction θ_(cent) FILT remains in the vehiclemoving lane area (4) since the delay direction (4) varies with a delaywith respect to the actual center angle θ_(cent) r.

As discussed above, the delay direction θ_(cent) FILT, which is theblunted value of the actual center angle θ_(cent) r, remains in thevehicle moving lane area (4) from the time the object 54 anterior to theradar equipped vehicle 52 enters the curve and until the radar equippedvehicle 52 exits the curve. Accordingly, it is possible to perform anaccurate determination for a curve moving condition includingimmediately before the entrance and immediately after the exit of thecurve by determining whether the object 54 and the vehicle 52 are in thesame lane based on whether or not the delay direction θ_(cent) FILTexists in the vehicle moving lane.

Now returning to FIG. 6, after the process of step 103 or steps 104 and105 is performed for all of the detected objects, and the object centerangle θ_(cent) is obtained for each of the objects, a process of step106 is performed. It is determined, in step 106, whether or not thecondition (vehicle moving lane condition) of the radar equipped vehiclelane area represented by the above-mentioned relationship (4) issatisfied for each of the detected objects. If it is determined that thevehicle moving lane condition is established for none of the objects,the routine is ended without performing any process. On the other hand,if it is determined that there is an object which satisfies the vehiclemoving lane condition, the routine proceeds to step 108. In step 108,the object which satisfies the vehicle moving lane condition isdetermined to be an object existing in the radar equipped vehicle movinglane, and then the routine is ended.

According to the above-mentioned method, it can be determined with anaccurate response as to whether or not an object newly entered in thedetectable range is in the radar equipped vehicle lane. Additionally, itcan be determined with high accuracy as to whether or not an objectcontinuously exists in the radar equipped vehicle lane, including thetime when the object and the vehicle enter and exit a curve.

In the above-mentioned embodiment, the digital filter is used forobtaining the blunted value as a method for providing a delay to theactual center angle θ_(cent) r to calculate the delay direction θ_(cent)FILT. However, the present invention is not limited to the use of adigital filter, and a predetermined delay may be provided to obtain thedelay direction θ_(cent) FILT by applying a known delay process to theactual center angle θ_(cent) r.

A description will now be given of a second embodiment of the presentinvention. The scan-type radar apparatus for a vehicle according to thesecond embodiment of the present invention has the same structure asthat of the radar apparatus according to the first embodiment shown inFIG. 1. In the radar apparatus according to the second embodiment, theradar ECU 30 performs a routine according to a flowchart shown in FIG.11 instead of the process according to the flowchart shown in FIG. 6.

In the above-mentioned first embodiment, it is always determined basedon the delay direction θ_(cent) FILT, which is a blunted value of theactual center angle θ_(cent) r, as to whether an object continuouslyexisting in the detectable range is in the radar equipped vehicle lane.According to this method, an accurate determination can be performed atan entrance and exit of a curve. However, a determination cannot beperformed with a quick response when an object moves from the radarequipped vehicle lane to the other lanes. The second embodiment ischaracterized in that a lane change of an object in the radar equippedvehicle lane can be detected with a quick response while an accuratedetermination of the existence of an object in the vehicle moving laneat the entrance and exit of a curve is maintained.

FIG. 11 is a control routine performed by the radar ECU 30 in the radarapparatus according to the second embodiment. In FIG. 11, steps that arethe same as the steps shown in FIG. 6 are given the same referencenumerals, and descriptions thereof will be omitted.

The routine shown in FIG. 11 is started each time the radar antenna 40scans from -10 degrees to +10 degrees. When it is determined, in step102, that there is an object existing in the previous data, the routineproceeds to step 110. In step 110, a blunted value θ_(cent) rsm iscalculated. The blunted value θ_(cent) rsm is obtained by filtering theactual center angle θ_(cent) r with a low-pass filter having arelatively high cut-off frequency such as 1 Hz.

In step 112, a change rate of the blunted value θ_(cent) rsm iscalculated. The blunted value θ_(cent) rsm quickly responds to a changein the actual center angle θ_(cent) r as compared to a response of thedelay direction θ_(cent) FILT. Accordingly, the blunted value θ_(cent)rsm exhibits a relatively quick change when the object performs a lanechange.

In step 114, it is determined whether the change rate dθrsm/dt of theblunted value θ_(cent) rsm generated during a period from the lastprocess to the current process is equal to or greater than apredetermined value Th1. The predetermined value Th1 is set to a valueso that the condition of step 114 is satisfied when the object performsa lane change. Accordingly, if it is determined that the condition ofstep 114 is not satisfied, it can be determined that the object does notperform a lane change. In this case, the routine proceeds to step 104 toobtain the delay direction θ_(cent) FILT based on the above-mentionedexpression (5). Then, in step 105, the delay direction θ_(cent) FILT isstored as an object center angle θ_(cent), and the routine proceeds tostep 106.

On the other hand, if it is determined, in step 114, that the changerate is equal to or greater than the predetermined value Th1, theroutine proceeds to step 116. It is determined, in step 116, whether ornot the change rate dθrsm/dt continuously exceeds for a predeterminedperiod of time Tm sec. If the determination of step 116 is negative, itcan be determined that a position of the object was temporarily changedand no lane change was performed. Thus, the routine proceeds to step 104to obtain the delay direction θ_(cent) FILT based on the above-mentionedexpression (5). Then, in step 105, the delay direction θ_(cent) FILT isstored as an object center angle θ_(cent), and the routine proceeds tostep 106.

If it is determined that the change rate dθrsm/dt continuously exceedsfor the predetermined period of time Tm sec, it can be determined thatthe object if in the process of changing the lane. In this case, theroutine proceeds to step 118 to substitute a value Ks, which is lessthan the standard value Kb used in the first embodiment, for theconstant K used in the above-mentioned relationship (4). In the presentembodiment, the value Ks is set to 0.7. The vehicle moving lane arearecognized by the radar ECU 30 is narrow as the constant K in therelationship (4) is small. Thus, when the process of step 118 isperformed, the vehicle moving lane area recognized by the radar ECU 30is narrower than that obtained when the standard value Kb is set to theconstant K.

After the process of step 118 is completed, the routine proceeds to step120. In step 120, the blunted value θ_(cent) rsm is substituted for theobject center angle θ_(cent), and the routine proceeds to step 116.Then, it is determined, in step 106, whether or not the object centerangle θ_(cent) satisfies the vehicle moving lane condition representedby the above-mentioned relationship (4). If it is determined that theradar equipped vehicle moving lane condition is satisfied by the objectcenter angle θ_(cent), the routine proceeds to step 108. In step 108,the object which satisfies the radar equipped vehicle moving lanecondition is determined to be an object in the radar equipped vehiclemoving lane.

On the other hand, if it is determined, in step 106, that the objectcenter angle θ_(cent) does not satisfy the radar equipped vehicle movinglane condition, the routine proceeds to step 122. In step 122, thestandard value Kb is substituted for the constant K used in theabove-mentioned relationship (4).

The control routine is ended when step 108 or step 122 is completed.

According to the above-mentioned control process, similar to the firstembodiment, the establishment of the radar equipped vehicle moving lanecondition is determined based on the delay direction θ_(cent) FILTcalculated by the expression (5) and the vehicle moving lane areadetermined by the standard value Kb when the blunted value θ_(cent) rsmof the object in the detectable range is gently changed such as at theentrance or exit of a curve. Accordingly, an accurate determination isperformed when the object and the radar equipped vehicle enter or exit acurve.

Additionally, when the object performs a lane change, the establishmentof the vehicle moving lane condition is determined based on the bluntedvalue θ_(cent) rsm which changes quickly as compared to the delaydirection θ_(cent) FILT calculated by the expression (5) and the vehiclemoving lane area determined by the standard value Ks which is less thanthe standard value Kb. In this process, the object changing the lane canbe eliminated quickly from the objects already existing in the radarequipped vehicle moving lane when the object moves from the radarequipped vehicle moving lane to another lane. Thus, in the presentembodiment, an accurate determination at an entrance or exit of a curveand a quick response for a determination of a lane change are compatiblewith each other at a high level.

A description will now be given, with reference to FIGS. 12 to 15, of athird embodiment of the present invention. A scan-type radar apparatusaccording the third embodiment of the present invention has the samestructure as that of the radar apparatus according to the firstembodiment shown in FIG. 1. In the radar apparatus according to thethird embodiment, the radar ECU 30 performs a routine according to aflowchart shown in FIG. 14 instead of the control process according tothe flowchart shown in FIG. 6 or FIG. 11.

FIG. 12 is an illustration of the radar equipped vehicle 52 and theobject 54 which moves to another lane during a period from a time t1 toa time t2 and returns to the radar equipped vehicle lane at a time t3.FIG. 13A is a graph showing a variation of the actual center angleθ_(cent) r when the object moves as mentioned above. FIG. 13B is a graphshowing a variation of the delay direction θ_(cent) FILT calculatedbased on the expression (5) and corresponding to the variation of theactual center angle θ_(cent) r shown in FIG. 13A. IT should be notedthat, θ_(Th) is a limit value of the vehicle moving lane area calculatedbased on the relationship (4).

In the above-mentioned first embodiment, all of the objects continuouslydetected in the detectable range are the objects of which lane isdetermined based on the object center angle θ_(cent) calculated based onthe expression (5). This method is effective to obtain an accuratedetermination performed at an entrance and exit of a curve. However, itis not possible to quickly detect an object entering from another laneto the radar equipped vehicle moving lane.

That is, as shown in FIG. 13A, the actual center angle θ_(cent) rdecreases to a value less than the limit value θ_(TH) immediately afterthe time t3 when the object 54 starts to return to the radar equippedvehicle moving lane. On the other hand, as shown in FIG. 13B, the objectcenter angle θ_(cent) r which is calculated based on the expression (5),reaches the limit value θ_(TH) at a time t4 which is a predeterminedperiod delayed from the time t3. Accordingly, if the moving lane isdetermined based on the object center angle θ_(cent), the detection ofthe object 54 is delayed a period t4-t3 from the detection based on theactual center angle θ_(cent) r.

The third embodiment is characterized in that an object entering fromanother lane can be can be detected with a quick response while anaccurate determination of the existence of an object in the vehiclemoving lane at the entrance and exit of a curve is maintained.

The routine shown in FIG. 14 is started at every time the scanningoperation is performed by the radar antenna 40 from -10 degrees to +10degrees of the scan angle θ_(S). In the routine shown in FIG. 14, afterthe actual center angle θ_(cent) r of each of the recognized objects iscalculated, in step 101, based on the grouped sets of data, the routineproceeds to step 124.

In step 124, it is determined whether or not the actual center angleθ_(cent) r satisfies the vehicle moving lane condition. If it isdetermined that the actual center angle θ_(cent) r satisfies the vehiclemoving lane condition, the routine proceeds to step 108 so that theobject corresponding to the actual center angle θ_(cent) stored as anobject existing in the radar equipped vehicle moving lane. On the otherhand, if it is determined, in step 124, that the actual center angleθ_(cent) r is out of the radar equipped vehicle moving lane area, theroutine proceeds to step 102.

In step 102, it is determined whether or not the current object detectedat this time exists in the sets of previous data. As a result, it can bedetermined that the current object is an object newly entered in thedetectable range but not existing in the radar equipped vehicle movinglane. Such an object is eliminated from the object to be processedwithout being applied with the process of step 108.

On the other hand, if it is determined, in step 102, that the objectexists in the sets of previous data, such an object can be determined tobe the object which was eliminated from objects existing in the radarequipped vehicle moving lane due to entry into a curve. Such an objectis subjected to the process for determining whether or not the delaydirection θ_(cent) FILT thereof satisfies the vehicle moving lanecondition. in steps 104 and 106.

If it is determined that the vehicle moving lane condition is satisfied,the routine proceeds to step 108 so that the object is recognized as anobject existing in the radar equipped vehicle moving lane. On the otherhand, if it is determined, in step 106, that the vehicle moving lanecondition is not satisfied, the object is eliminated from objects to beprocessed without being subjected to the process of step 108. Thecontrol routine is ended after each of the above-mentioned processes isperformed for each of the detected objects.

FIG. 15A illustrates, similar to FIG. 13A, a variation of the actualcenter angle θ_(cent) r of the object 54. FIG. 15B illustrates avariation of a determination value used for determining an establishmentof the vehicle moving lane condition in the present embodiment. Thedetermination value is a combination of the actual center angle θ_(cent)r and the delay direction θ_(cent) FILT.

As shown in FIG. 15B, according to the above-mentioned process, when theobject 54 is continuously detected in the vehicle moving lane area, itis determined whether the object 54 satisfies the vehicle moving lanecondition based on the delay direction θ_(cent) FILT. Accordingly, anaccurate determination can be made, similar to the first embodiment,when the object 54 enters and exits a curve. Additionally, when theobject 54 is entering from another lane, it is determined whether or notthe object 54 satisfies the vehicle moving lane condition based on theactual center angle θ_(cent) r. Thus, according to the presentembodiment, an object entering the radar equipped vehicle lane fromanother lane can be detected with a quick response.

A description will now be given, with reference to FIGS. 16 to 20, of afourth embodiment of the present invention. A scan-type radar apparatusaccording to the fourth embodiment of the present invention has the samestructure as that of the radar apparatus according to the firstembodiment shown in FIG. 1. In the radar apparatus according to thefourth embodiment, the radar ECU 30 performs a routine according to aflowchart shown in FIGS. 18 to 20 instead of the control processaccording to the flowchart shown in FIG. 6, FIG. 11 or FIG. 14.

The radar apparatus according to the fourth embodiment of the presentinvention is characterized in that a determination of an object enteringa curve is made based on a detection as to whether a plurality ofobjects existing anterior of the radar equipped vehicle show the samemovement.

FIG. 16 is an illustration of the radar equipped vehicle and a pluralityof objects including the object 54 existing in the radar equippedvehicle lane and objects 56 and 58 moving in other lanes. The objects 56and 58 may be hereinafter referred to as other lane objects. In FIG. 16,the radar equipped vehicle 52 is just entering a curve. The other laneobject 58 is moving between the object 54 and the radar equipped vehicle52. The other lane object 56 is moving ahead of the object 54.

FIG. 17 is a graph showing a variation of the actual center angleθ_(cent) r detected by the radar equipped vehicle 52 with respect toeach of the objects 54, 56 and 58. As shown in FIG. 16, when the objects56, 54 and 58 enter the curve in that order, the actual center angleθ_(cent) r of each of the objects changes with a time delay in the samedirection. Accordingly, when such variation of the actual center angleθ_(cent) r is detective in a plurality of objects, it is determined thatthe objects 54, 56 and 58 entered or exited a curve.

In the present embodiment, when it is determined that the a plurality ofobjects anterior to the radar equipped vehicle 52 enter or exit thecurve based on the movement of the objects, the object 54 is determinedto exist in the radar equipped vehicle lane for a predetermined periodirrespective of whether the actual center angle θ_(cent) r or the delaydirection θ_(cent) FILT of the object 54 is in the radar equippedvehicle moving lane. Accordingly, an erroneous determination that theobject 54 moved to another lane can be prevented when the object 54entered into the curve.

FIGS. 18 to 20 are parts of a flowchart of a control routine performedby the radar ECU 30. In FIGS. 18 to 20, steps that are the same as thesteps shown in FIG. 11 are given the same reference numerals, anddescriptions thereof will be omitted. The control routine shown in FIGS.18 to 20 is started each time the radar antenna scans -10 degrees to +10degrees.

When the control routine is started, the actual center angle θ_(cent) ris calculated, in steps 100 and 101, for each of the detected objectsanterior to the radar equipped vehicle 52. The blunted value θ_(cent)rsm and the change rate dθrsm/dt is calculated in steps 102, 110 and 112with respect to the objects continuously detected from the previousprocess. After the above process is completed, the routine proceeds tostep 126.

In step 126, it is determined whether or not the turning radius of thevehicle 52 is maintained to be a constant value. If the turning radiusfluctuates and is not maintained to be a constant value, it isdetermined that the vehicle 52 is moving at the entrance or the exit ofthe curve. In the routine, the process of the steps 128 to 152 isprovided for determining movement of the object 54 when the radarequipped vehicle 52 is moving straight or turning in the middle of acurve.

Accordingly, when the vehicle 52 is moving at the entrance or the exitof the curve, the process of steps 128 to 125 should not be performed.Thus, when it is determined that the turning radius of the vehicle 52 isnot constant, the process of steps 128 to 152 is skipped, and theprocess of step 114 shown in FIG. 18 is performed. On the other hand, ifit is determined, in step 126, that the turning radius of the vehicle 52is maintained to be constant, the routine proceeds to step 128.

In step 128, it is determined whether or not a flag FCV1 is set to "1".The flag FCV1 represents a relatively large change rate dθrsm/dt beingdetected in one of the objects anterior to the vehicle 52. Thus, whenthe large change rate dθrsm/dt has not been detected in the previousprocess, the flag FCV1 is not set to "1". In this case, the routineproceeds to step 130.

In step 130, it is determined whether or not there is an object havingthe blunted value θ_(cent) rsm is varied at a change rate greater than apredetermined value Th2. The predetermined value Th2 is set to a valueso that a relationship dθrsm/dt≧Th2 is satisfied when a remote objectmoving in a position away from the vehicle 52 enters the curve. Thedistance between the remote object and the vehicle 52 is, for example,about 70 m.

If it is determined, in step 130, that there is no object satisfying therelationship dθrsm/dt≧Th2, it is determined that there is no objectwhich entered a curve or changed a lane. In this case, the process ofsteps 132 to 152 is skipped, and the routine proceeds to step 114. Onthe other hand, if it is determined, in step 132, that there is anobject which satisfies the relationship dθrsm/dt≧Th2the, it isdetermined that there is an object which entered a curve or changed alane. In this case, the routine proceeds to step 132. In FIG. 16, theobject 56 corresponds to the object which satisfies the relationshipdθrsm/dt≧Th2.

In step 132, a time t0 when the process of step 132 is started isstored. Additionally, a relative distance RD1 between the vehicle 52 andthe object 56, a relative velocity RVi of the object 56 with respect tothe vehicle 52 and an inter-object distance dRD1i between the object 56and one of other objects are stored at the tine t0. It should be notedthat "i" of RVi and dRD1i indicates a number provided to each of aplurality of objects. After the above-mentioned process is completed,the routine proceeds to step 134.

In step 134, the flag FCV is set to "1". Then, in step 136, a timer T1is started. The timer T1 is provided for timing a period starting at atime when a change which satisfies the relationship dθrsm/dt≧Th2 isrecognized in one of the objects. After the process of step 136 iscompleted, the routine proceeds to step 114 shown in FIG. 18.

If the present routine is started after the flag FCV is set to "1", itis determined, in step 128, that the flag FCV1 is set to "1". Thus, inthis case, the routine proceeds to step 137. In step 137, it isdetermined whether or not a flag FCV2 is set to "1". The flag FCV2 isset to "1" when the relationship dθrsm/dt≧Th2 is satisfied with respectto one of the object excluding the object 56. If it is determined thatthe flag FCV2 is not set to "1", the routine proceeds to step 138.

In step 138, it is determined whether or not there is an object, whichhas a change rate greater than the predetermined value Th2 and theblunted value being varied, among the objects excluding the object 56.If it is determined that there is no object which satisfies the abovecondition, it is determined that there is no object whose movement issimilar to the movement of the object 56. In this case, the routineproceeds to step 114. On the other hand, if it is determined that thereis such an object which satisfies the above condition, it is determinedthat there is an object whose movement is similar to the movement of theobject 56. In this case, the routine proceeds to step 140. In FIG. 16,the object 54 corresponds to the object whose movement is similar to themovement of the object 56.

In step 140, the time t1 when the process of step 140 is started, thatis, the time when the condition of step 138 is established, is stored.After the process of step 138 is completed, the routine proceeds to step142.

In step 142, it is determined whether or not the time difference "t1-t0"between the time t1 and the time t0 is approximately equal to an assumedtime difference dRD12/V2. The assumed time difference dRD12/V2 is aperiod of time obtained by dividing the inter-object distance dRD12,which was formed between the objects 56 and 54 at the time t0, by anabsolute velocity V of the object 54. The absolute velocity V2 of theobject 54 is calculated by adding the relative velocity RV2 of theobject 54 at the time t0 to the velocity V of the vehicle 52.Accordingly, the assumed time difference dRD12/V2 corresponds to theperiod from the time t0 to the time when the object 54 reaches theentrance or the exit of the curve.

If it is determined that the time difference "t1-t0" is approximatelyequal to the assumed time difference "dRD12/V2", it can be determinedthat the movement of the object 54 and the movement of the object 56 aresimilar to each other. In this case, the routine proceeds to step 144.On the other hand, if it is determined, in step 142, that the timedifference "t1-t0" is different from the assumed time difference"dRD12/V2", it is determined that the movement of the object 54 and themovement of the object 56 are not similar to each other. In this case,the process of step 144 is skipped and the routine proceeds to step 114shown in FIG. 18.

In step 144, the flag FCV2 is set to "1". Then, the routine proceeds tostep 114.

If the present routine is started after the flag FCV2 is set to "1", itis determined, in step 136, that the flag FCV2 is set to "1". In thiscase, the routine proceeds to step 146.

In step 146, it is determined whether or not there is an object whoseblunted value θ_(cent) rsm is changed at a change rate dθrsm/dt greaterthan the predetermined value Th2 among objects excluding the objects 54and 56. If it is determined that there is no object which satisfies theabove condition, it is determined that there is no object which shows amovement similar to the movement of the objects 54 and 56. In this case,the routine proceeds to step 114 shown in FIG. 18. On the other hand, ifit is determined that there is an object which satisfies the conditiondθrsm/dt≧Th2, it is determined that there are three objects anterior tothe vehicle 52 which objects show a movement to each other. In thiscase, the routine proceeds to step 148. In FIG. 16, the object 58corresponds to the object which satisfies the above condition.

In step 148, the time t1 when the process of step 148 is started, thatis, when the condition of step 146 is established, is stored. After thisprocess is completed, the routine proceeds to step 150.

In step 150, it is determined whether or not the time difference "t2-t0"between the time t2 and the time t0 is approximately equal to an assumedtime difference dRD13/V3. The assumed time difference dRD13/V3 is aperiod of time obtained by dividing the inter-object distance dRD13,which was formed between the objects 56 and 58 at the time t0, by anabsolute velocity V3 of the object 58. The absolute velocity V3 of theobject 58 is calculated by adding the relative velocity RV3 of theobject 58 at the time t0 to the velocity V of the vehicle 52.Accordingly, the assumed time difference dRD13/V3 corresponds to theperiod from the time t0 to the time when the object 58 reaches theentrance or the exit of the curve.

If it is determined that the time difference "t2-t0" is approximatelyequal to the assumed time difference "dRD13/V3", it can be determinedthat the movement of the object 58 and the movement of the object 56 aresimilar to each other. In this case, the routine proceeds to step 152.On the other hand, if it is determined, in step 150, that the timedifference "t2-t0" is different from the assumed time difference"dRD13/V3", it is determined that the movement of the object 58 and themovement of the object 56 are not similar to each other. In this case,the process of step 152 is skipped and the routine proceeds to step 114shown in FIG. 18.

In step 152, a flag FCVIN is set to "1". Then, the routine proceeds tostep 114. As mentioned above, in this routine, the flag FCVIN is set to"1" when there is at least three objects showing a similar movement inthe area anterior to the radar equipped vehicle 52.

When the three objects existing in the anterior area of the vehicle 52show a similar movement with a time difference corresponding to theinter-object distance RD1i, it is determined with a high probabilitythat the three objects sequentially entered or exited the curve.Accordingly, in this routine, when the flag FCVIN is equal to 1, it isdetermined with a high probability that the object 54 entered or exitedthe curve.

In steps 114 to 120, 104 and 105, similar to the second embodiment, thestandard value Ks which is smaller than the standard value Kb issubstituted for the constant K. additionally, the object center angleθ_(cent) is substituted for the actual center angle θ_(cent) r, or theobject center angle θ_(cent) is substituted for the delay directionθ_(cent) FILT. After these processes are completed, the routine proceedsto step 154.

In step 154, it is determined whether or not the flag FCVIN is set to"1". The condition of step 154 is not established when it is not assumedthat the object 54 entered or exited the curve based on the movement ofa plurality of objects. In this case, the routine proceeds to step 106so as to determine whether the vehicle moving lane condition isestablished, similar to the second embodiment.

After the process of step 106 is completed, the routine proceeds to step108 or step 122 depending on the result of determination of step 106,and the routine is ended. In this process, it is determined whether ornot the object 54 exists in the radar equipped vehicle moving areasimilar to the second embodiment.

If it is determined, in step 154, that the flag FCVIN is set to "1", theroutine proceeds to step 156. In step 156, a curve reaching time T0 iscalculated. The curve reaching time T0 is a period of time which will bespent by the vehicle 52 to reach at the position of the object 56 atwhich position the movement satisfying the relationship dθrsm/dt≧Th2 isrecognized in the object 56. In this routine, the curve reaching time T0is calculated by dividing the relative distance RD1 by the velocity V ofthe vehicle 52, the relative distance RD1 being a distance between theobject 56 and the vehicle 52 at the time t0. After T0=RD1/V iscalculated, the routine proceeds to step 158.

In step 158, it is determined whether or not the time indicated by thetimer T1, which is started at the time t0, has reached a sum of thecurve reaching time T0 and a predetermined time value δ. If the changein the movement of the object 56 at the time t0 is caused by the object56 entering or exiting the curve, it is determined that the object 56 isat the entrance or exit of the curve at the time t0. In this case, thetime t0+T0 corresponds to the time when the vehicle 52 reaches theentrance or exit of the curve.

When the object 54, which was determined to exist in the radar equippedvehicle moving lane, is moving behind the object 54, the object 54reaches the entrance or exit of the curve at the time t2 which isbetween the time t0 and the time t0+T0. If the object 54 is the remoteobject which is moving a relatively long distance away from the vehicle52, there is a large time difference between the time t2 and the timet0+T0.

The delay direction θ_(cent) FILT calculated for the object 54 begins tovary gently while following the variation of the actual center angleθ_(cent) r after the actual center angle θ_(cent) r begins to vary. Onthe other hand, the vehicle moving lane area obtained in accordance withthe above-mentioned relationship (4) is maintained to be an areacorresponding to the straight lane until the time t0+T0 is reached.After the time t0+T0 is reached, the vehicle moving lane area iscorrected to an area in accordance with the turning radius of thevehicle 52.

When the time difference between the time t2 when the actual centerangle θ_(cent) r begins to vary and the time t0+T0 when the vehiclemoving lane area begins to be corrected is not sufficiently large, thecorrection of the vehicle moving lane area is started prior to the delaydirection θ_(cent) FILT shifting out of the vehicle moving lane area. Inthis case, the result of determination as to whether the delay directionθ_(cent) FILT exists in the vehicle moving lane area accurately matchesthe fact as to whether the object 54 is existent in the vehicle movinglane.

However, if the object 54 is the remote object and the time differencebetween the time t1 and the time t0+T0 is large, The delay directionθ_(cent) FILT may be shifted out of the vehicle moving lane area beforethe correction to the vehicle moving lane area is started. In this case,depending on a determination logic for determining the vehicle movinglane, there is a possibility of an erroneous determination that theobject 54 does not exist in the vehicle moving lane despite that theobject 54 is actually moving in the vehicle moving lane.

The predetermined time value δ used in step 158 is set to a time periodnecessary for correcting the vehicle moving lane area after the vehicle52 reached the entrance or exit of the curve. Accordingly, if it isdetermined, in step 158, that the relationship T1≧T0+δ is not satisfied,it is recognized that the correction to the vehicle moving lane area hasnot been performed yet despite the fact that the object 54 has alreadyreached the entrance or exit of the curve. In this case, if the delaydirection θ_(cent) FILT should be shifted out of the vehicle moving lanearea, it is appropriate to determine that the object 54 exists in thevehicle moving lane. In this routine, when such a determination is madein step 158, the routine proceeds to step 160.

In step 160, the objects which were determined to exist in the vehiclemoving lane are determined to continuously exist in the vehicle movinglane, and the routine is ended. According to the above-mentionedprocess, exclusion of the object is prevented from the objects existingin the vehicle moving lane due to the determination that the correctionto the vehicle moving lane has not been started after the object, whichwas determined to exist in the vehicle moving lane in the previousprocess, entered in the curve.

If it is determined, in step 158, that the relationship T1≧T0+δ issatisfied, it is recognized that the correction to the vehicle movinglane area has been performed so that the vehicle moving lane area iscorrected to an area corresponding to the radius of curvature of thearea between the vehicle and the object 54 after the object 54 passesthe entrance or exit of the curve. When the vehicle moving lane isproperly corrected, it is appropriate to determine whether or not theobject exists in the vehicle moving lane based on the determination asto whether the object center angle θ_(cent) satisfies the vehicle movinglane condition. If the above determination is made in step 158, theroutine proceeds to step 162.

In step 162, the flags FCV1, FCV2 and FCVIN are reset to "0", and thetimer T1 is cleared. Then, the routine proceeds to step 106 so that thedetermination is performed as to the condition of the vehicle movinglane condition based on the object center angle θ_(cent). According tothe above-mentioned process, is can be determined whether or not anobject exists in the radar equipped vehicle moving lane in the samemanner as the second embodiment when the correction is made to thevehicle moving lane area.

In the present embodiment, the determination of the object 54 entering acurve is made by referring to the similarity of movement of the threeobjects 54, 56 and 58. However, the determination may be made byreferring to the similarity of movement of two objects or more thanthree objects.

A description will now be given, with reference to FIGS. 21 to 23, of afifth embodiment of the present invention. A scan-type radar apparatusaccording to the fifth embodiment of the present invention has the samestructure as that of the radar apparatus according to the firstembodiment shown in FIG. 1. In the radar apparatus according to thefifth embodiment, the radar ECU 30 performs a routine according to aflowchart shown in FIGS. 22 and 23 instead of the control processaccording to the flowchart shown in FIG. 6, FIG. 11, FIG. 14 or FIGS. 18to 20.

The radar apparatus according to the fifth embodiment of the presentinvention is characterized in that the objects anterior to the vehicle52 are classified into a short distance object group, a middle distanceobject group and a long distance object group so that a determination ofan establishment of the vehicle moving lane condition is performed basedon the classification.

FIG. 21 is a graph showing variation of the actual center angle θ_(cent)r of an object when the object enters a curve or changes a lane. In FIG.21, a solid line (1) indicates a variation with respect to a shortdistance object entering a curve, the short distance object being about20 m apart from the vehicle 52. A dashed line (2) indicates a variationwith respect to the short distance object changing a lane. A solid line(4) indicates a variation with respect to a long distance objectentering a curve, the long distance object being about 80 m apart fromthe vehicle 52. A dashed line (3) indicates a variation with respect tothe short distance object changing a lane.

When the short distance object and the long distance object move in adirection perpendicular to a side-to-side direction of the object, thevariation in the actual center angle θ_(cent) r of the short distanceobject is greater than that of the long distance object. Accordingly,when the short distance object enters a curve or changes a lane, theactual center angle θ_(cent) r of the short distance object is variedfaster than the actual center angle θ_(cent) r of the long distanceobject.

The relative distance between the object and the vehicle 52 varies by awidth of a lane during a lane change of the object. The upper limit (aflat portion) of the dashed line (2) of the actual center angle θ_(cent)r of the short distance object corresponds to a variation caused by theshort distance object being moved by the width of the lane. The upperlimit (a flat portion) of the dashed line (3) of the actual center angleθ_(cent) r of the long distance object corresponds to a variation causedby the long distance object being moved by the width of the lane.

After the object enters the curve, the actual center angle θ_(cent) r ofthe object continues to vary until the vehicle 52 enters into the curve.If the object is the short distance object, the vehicle 52 enters thecurve in a short time after the object enters the curve. Accordingly, asshown in the solid line (1), the actual center angle θ_(cent) r of theshort distance object reaches a relatively small value. On the otherhand, if the object is the long distance object, the vehicle 52 entersthe curve after a relatively long period of time has passed since theobject entered the curve. Accordingly, as shown in the solid line (4),the actual center angle θ_(cent) r of the long distance object reaches arelatively large value.

As mentioned above, according to the present embodiment, the object inthe vehicle moving lane can be discriminated from among a plurality ofobjects existing ahead of the vehicle 52. If the objects in the vehiclemoving lane can be distinguished, it is easy to extract the object whichis closest to the vehicle 52 from among the distinguished objects.Hereinafter, the object closest to the vehicle 52 may be referred to asa first object. For example, if an operation of the vehicle iscontrolled so that a distance between the vehicle 52 and the firstobject is a predetermined distance, a safe operation of the vehicle 52can be achieved when the vehicle 52 is automatically operated. Thus, theradar apparatus according to the present embodiment can be applied to anautomatic vehicle guidance control system.

When the operation of the vehicle 52 is automatically guided, in orderto achieve a quick response, it is preferable to have a capability ofperforming an acceleration immediately after the short distance objectin the vehicle moving lane has moved to another lane. In this respect,the radar apparatus is required a function to detect a lane change ofthe short distance object.

As shown in FIG. 21, when the short distance object changes a lane, theactual center angle θ_(cent) r changes for a relatively long period oftime as compared to the actual center angle θ_(cent) r obtained when theshort distance object enters into a curve. Accordingly, it is determinedthat the short distance object changed a lane when the actual centerangle θ_(cent) r changes for a sufficiently long period of time with arelatively large change rate such as obtained when entering a curve orchanging a lane. The radar apparatus according to the present embodimenthas a function to perform a quick detection of the lane change of theshort distance object according to the above-mentioned method.

As discussed previously, when the long distance object enters a curve,the delay direction θ_(cent) FILT is shifted out of the vehicle movinglane area irrespective of the object existing in the vehicle movinglane. Accordingly, if a determination based on the delay directionθ_(cent) FILT is performed for the long distance object as well as themiddle distance object, a sufficient accuracy of the determinationcannot be obtained.

As shown in FIG. 21, when the long distance object enters a curve, theactual center angle θ_(cent) r of the long distance object shows a sharpvariation as compared to the actual center angle θ_(cent) r obtainedwhen the long distance object changes a lane. Accordingly, it isdetermined that the long distance object entered a curve when the actualcenter angle θ_(cent) r changes continuously for a sufficiently longperiod of time sufficient for determining that the object enters a curveor changes a lane with a relatively large change rate. The radarapparatus according to the present embodiment has a function to maintainthe long distance object as an object existing in the vehicle movinglane when the long distance object is assumed to enter a curve by theabove-mentioned method.

FIGS. 22 and 23 are parts of a flowchart of a control routine performedby the radar ECU 30. In FIGS. 22 and 23, steps that are the same as thesteps shown in FIG. 11 are given the same reference numerals, anddescriptions thereof will be omitted. The control routine shown in FIGS.22 and 23 is started each time the radar antenna scans -10 degrees to+10 degrees.

When the control routine is started, the actual center angle θ_(cent) ris calculated, in steps 100 and 101, for each of the detected objectsanterior to the radar equipped vehicle 52. The blunted value θ_(cent)rsm and the change rate dθrsm/dt is calculated in steps 102, 110 and 112with respect to the objects continuously detected from the previousprocess. After the above process is completed, the routine proceeds tostep 164.

In step 164, it is determined whether or not the object (hereinafterreferred to as a current object) currently being processed is the longdistance object which is a long distance away from the vehicle 52. Instep 164, an object having the relative distance RDi of more than 70 mis determined to be the long distance object. If it is determined thatthe current object is not the long distance object, the routine proceedsto step 166.

In step 166, is determined whether or not the current object is theshort distance object which is a short distance away from the vehicle52. In step 166, an object having the relative distance RDi of less than30 m is determined to be the short distance object. If it is determinedthat the current object is not the short distance object, the routineproceeds to step 114. Accordingly, in the present embodiment, the middledistance object is subjected to the processed of step 114.

After step 114, the same process as the second embodiment is performed.With regard to the middle distance object, the result of determinationas to whether the delay direction θ_(cent) FILT exists in the vehiclemoving lane area accurately matches the fact whether the object existsin the vehicle moving lane. Thus, in the radar apparatus according tothe present embodiment, it is accurately determined whether or not themiddle distance object exists in the vehicle moving lane.

If it is determined, in step 168, that the current object is the shortdistance object exists in the vehicle moving lane, the routine proceedsto step 168.

In step 168, it is determined whether or not the change rate dθrsm/dt ofthe blunted value θ_(cent) rsm with respect to the current object isequal to or greater than a predetermined value Thn. the predeterminedvalue Thn is a value slightly smaller than the change rate dθrsm/dtwhich is obtained when the short distance object changes a lane or whenthe short distance object enters or exits a curve.

Accordingly, if it is determined that the above-mentioned relationshipis not satisfied, it is determined that the object is not changing alane or entering or exiting a curve. When such a determination is madein step 168, the routine proceeds to step 104 to perform the process todetermine whether or not the current object satisfies the vehicle movinglane condition based on the delay direction θ_(cent) FILT. On the otherhand, if it is determined, in step 168, that the relationshipdθrsm/dt≧Thn is satisfied, it is determined that the current object ischanging a lane or entering or exiting a curve. In this case, theroutine proceeds to step 170.

In step 170, it is determined whether or not the relationship of step168 is continuously satisfied for a predetermined time period Tn. Thepredetermined time period Tn is a period of time which is shorter than aperiod during which the blunted value θ_(cent) rsm is continuouslychanged when the short distance object changes a lane. Additionally, thepredetermined time period Tn is longer than the period during which theblunted value θ_(cent) rsm is continuously changed when the shortdistance object enters or exits a curve.

Accordingly, if it is determined that the above-mentioned relationshipof step 170 is not satisfied, it is determined that the object is notentering or exiting a curve. Thus, when such a determination is made instep 170, the routine proceeds to step 104 to perform the process todetermine whether or not the current object satisfies the vehicle movinglane condition based on the delay direction θ_(cent) FILT. On the otherhand, if it is determined, in step 170, that the relationship of step168 dθrsm/dt≧Thn is continuously satisfied for the predetermined timeperiod Tn, it is determined that the current object is changing a lane.In this case, the routine proceeds to step 172.

In step 172, it is determined whether or not the turning radius of thevehicle 52 is maintained to be approximately constant for apredetermined time period α sec after the relationship dθrsm/dt≧Thn issatisfied for the current object. The predetermined time period α sec isslightly longer than a time period necessary for the vehicle 52 to movethe distance between the current object and the vehicle 52. When thecurrent object is moving in the vehicle moving lane, the vehicle 52 issubjected to the same change which occurred in the current object beforethe predetermined time period has passed since the change occurred inthe current object.

The condition of step 172 is determined not to be established when thepredetermined time period α sec has not passed since the changesatisfying the relationship dθrsm/dt≧Thn occurred or a change occurredin the turning radius of the vehicle 52 before the predetermined timeperiod α sec has passed. Under such condition, a possibility of thecurrent object existing in the vehicle moving lane cannot be denied.Thus, if it is determined that the condition of step 172 is notestablished, the routine proceeds to step 104 to perform the process todetermine whether or not the current object satisfies the vehicle movinglane condition based on the delay direction θ_(cent) FILT. On the otherhand, if it is determined, in step 172, that the turning radius of thevehicle 52 is constant for the predetermined time period α sec, it isdetermined that the current object does not exist in the vehicle movinglane. In this case, the routine proceeds to step 174.

In step 174, the current object is excluded from the objects determinedto exist in the vehicle moving lane, and the routine is ended. Theobjects determined to exist in the vehicle moving lane may be referredto as vehicle moving lane objects. In the above-mentioned process, theshort distance object which has the blunted value subject to largechanges and for a long period of time is immediately excluded from thevehicle moving lane objects. Thus, in the radar apparatus according tothe present embodiment, the short distance object which changed a lanecan be immediately excluded from the vehicle moving lane objects.

If it is determined, in step 164, that the current object is the longdistance object, the routine proceeds to step 175. Then, in step 175, itis determined whether or not the current object was determined to be thevehicle moving lane object in the previous process. If it is determinedthat the current object was not determined to be the vehicle moving laneobject, the routine proceeds to step 104 to perform the process todetermine whether or not the current object satisfies the vehicle movinglane condition based on the delay direction θ_(cent) FILT. On the otherhand, if it is determined that the current object was determined to bethe vehicle moving lane object in the previous process, the routineproceeds to step 176. Hereinafter, the long distance object which wasdetermined to be the vehicle moving lane object in the previous processmay be referred to as a vehicle moving lane long distance object.

In step 176, it is determined whether or not the change rate dθrsm/dt ofthe blunted value θ_(cent) rsm with respect to the current object isequal to or greater than a predetermined value Thf. The predeterminedvalue Thf is a value smaller than the change rate dθrsm/dt which occurswhen the long distance object enters or exits a curve, and greater thanthe change rate dθrsm/dt which occurs when the long distance objectchanges a lane. Accordingly, if it is determined that theabove-mentioned relationship is satisfied, it is determined that thecurrent object, which is the long distance object, is entering orexiting a curve. In this case, the routine proceeds to step 178.

In step 178, it is determined whether or not the relationship of step176 is continuously satisfied for a predetermined time period Tf. Thepredetermined time period Tf is a period of time which is slightlyshorter than a period during which the blunted value θ_(cent) rsm iscontinuously changed when the long distance object enters or exits acurve. Accordingly, if it is determined that the above-mentionedrelationship of step 178 is satisfied, it is determined that the vehiclemoving lane long distance object is entering or exiting a curve. In thiscase, the routine proceeds to step 180.

In step 180, a flag FTRAC is set to "1". The flag FTRAC is provided forindicating that a movement of the current object, which is the vehiclemoving lane long distance object, entering or exiting a curve isrecognized. Hereinafter, the movement of an object entering or exiting acurve may be referred to as curve movement. After the process of step180 is completed, the routine proceeds to step 182.

In step 182, a value of a timer Tf is incremented. The timer Tf isprovided for timing an elapsed time after "1" is set to the flag FTRAC,that is, after the curve movement is recognized for the vehicle movinglane long distance object. As will be described later, the value of thetimer Tf is always reset to "0" while the flag FTRAC is set to "0".After the process of step 182 is completed, the routine proceeds to step184.

In step 184, the current object is determined to be the vehicle movinglane object, and the routine is ended. As mentioned above, in thisroutine, the vehicle moving lane long distance object showing the curvemovement is not subjected to the determination process based on thedelay direction θ_(cent) FILT, and is determined to be the vehiclemoving lane object.

If the result of determination of step 176 or step 178 is negative, thatis, if the current object, which is the vehicle moving lane longdistance object, does not show the curve movement, the routine proceedsto step 186.

In step 186, it is determined whether or not the flag FTRAC is set to"1". When the curve movement is recognized for the current object priorto the execution of the process of step 186, the flag FTRAC has alreadybeen set to "1". Thus, in this case, it is determined that the flagFTRAC is equal to "1", and the routine proceeds to step 188.

In step 188, the timer Tf is incremented. Since the timer Tf isincremented each time the routine proceeds to step 182 or step 188, thevalue of the timer Tf corresponds to the elapsed time period after thecurve movement was first recognized in the current object. After theprocess of step 188 is completed, the routine proceeds to step 190.

In step 190, it is determined whether or not the value of the timer Tfreaches a predetermined time period β. The predetermined time period βis a period from the time when the long distance object reaches anentrance or exit of a curve to the time when the vehicle 52 reaches theentrance or exit of the curve and when the vehicle moving lane area iscorrected to an area corresponding to a new turning radius. If it isdetermined, in step 190, that the relationship Tf≧β is not satisfied, itis determined that an appropriate correction to the vehicle moving lanearea has not been performed yet. In this case, the routine proceeds tostep 192 in which it is determined whether or not a predetermined changehas occurred in the turning radius of the vehicle 52. In the presentembodiment, when the turning radius of the vehicle 52 begins to change,the correction of the vehicle moving lane area is started. It isdetermined, in step 192, that the predetermined change has occurred inthe turning radius when it is recognized that a change sufficient forcorrecting the vehicle moving lane to an appropriate area has occurred.Accordingly, if it is determined that the predetermined change has notoccurred, it is determined that the vehicle moving lane area has notbeen corrected to an appropriate area. If such a determination is made,the routine proceeds to step 184.

According to the above-mentioned process, the vehicle moving lane longdistance object is continuously recognized as the vehicle moving laneobject without being subject to the determination process based on thedelay direction θ_(cent) FILT after the curve movement is recognized anduntil the predetermined time period β has passed or until thepredetermined change occurs in the turning radius of the vehicle 52.This is because if the object is subjected to the determination processbased on the delay direction θ_(cent) FILT, there is a possibility thatthe vehicle moving lane long distance object is excluded from thevehicle moving lane object after the vehicle moving lane long distanceobject entered or exited a curve. However, in the present embodiment,such an undesired process can be eliminated as discussed above. Thus, inthe radar apparatus according to the present embodiment, a furtheraccurate determination can be achieved as compared to the case where anestablishment of the vehicle moving lane condition with respect to thevehicle moving lane long distance object is determined based on thedelay direction θ_(cent) FILT.

If it is determined that the flag FTRAC is not set to "₁ " in step 186,or the relationship Tf≧β is satisfied in step 190, or the predeterminedchange has occurred in the turning movement of the vehicle 52 in step192, the routine proceeds to step 194 and consequently to step 196. Instep 194, the timer Tf is reset. IN step 196, the flag FTRAC is reset to"0". Thereafter, the routine proceeds to step 104 to perform the processto determine whether or not the current object satisfies the vehiclemoving lane condition based on the delay direction θ_(cent) FILT.

As discussed above, in the radar apparatus according to the presentembodiment, the short distance object is excluded from the vehiclemoving lane object immediately after the short distance object changed alane, and also the vehicle moving lane long distance object is treatedas the vehicle moving lane object during the predetermined period afterthe vehicle moving lane long distance object entered or exited a curve.Thus, the radar apparatus according to the present embodiment canachieve an automatic guided vehicle system with an accurate control.

A description will now be given, with reference to FIGS. 24 and 25, of asixth embodiment of the present invention. A scan-type radar apparatusaccording to the sixth embodiment of the present invention has the samestructure as that of the radar apparatus according to the firstembodiment shown in FIG. 1. In the radar apparatus according to thesixth embodiment, the radar ECU 30 performs a routine according to aflowchart shown in FIGS. 24 and 25 instead of the control processaccording to the flowchart shown in FIG. 6, FIG. 11, FIG. 14, FIGS. 18to 20 or FIGS. 22 and 23.

When a plurality of objects exist ahead of the vehicle 52 equipped withthe radar apparatus shown in FIG. 1, a plurality of vehicle moving laneobjects may be recognized. Among the vehicle moving lane objects,movement of the first object, which is closest to the vehicle 52, ismost important.

When the curve movement is shown for the first object, an erroneousdetermination may be made that the first object moved from the vehiclemoving lane to another lane. If such a determination is made under thecondition where a plurality of objects exist ahead of the vehicle 52,one of the other object will be determined to be the first object. Thismay decrease controllability of the automatic vehicle guide system suchthat an unnecessary deceleration is performed. The present embodiment ischaracterized in that the above-mentioned erroneous determination of thefirst object is eliminated.

FIGS. 24 and 25 are parts of a flowchart of a control routine performedby the radar ECU 30. In FIGS. 24 and 25, steps that are the same as thesteps shown in FIG. 11 are given the same reference numerals, anddescriptions thereof will be omitted. The control routine shown in FIGS.24 and 25 is started each time the radar antenna scans -10 degrees to+10 degrees.

When the control routine is started, the process of steps 100 to 122 isperformed. That is, it is determined whether or not each of the detectedobjects anterior to the radar equipped vehicle 52 corresponds to thevehicle moving lane object. Thereafter, the routine proceeds to step 200shown in FIG. 24.

In step 200, the first object is selected from among all of the objectsdetermined to be the vehicle moving lane objects. In this step, thevehicle moving lane object which is closest to the vehicle 52 isselected as the first object. After the process of step 200, the routineproceeds to step 202.

In step 202, it is determined whether or not the object (hereinafterreferred to as a previous first object) determined to be the firstobject in the previous process corresponds to the object (hereinafterreferred to as a present first object) determined to be the first objectin the present process. It is determined that the present first objectcorresponds to the previous first object when the relative distance RDiand the relative velocity RV of the previous first object do notsignificantly differ from those of the present first object.

If it is determined, in step 202, that the previous first object is notthe same with the present first object, it is determined that there is apossibility that one of the vehicle moving lane objects other than thetrue first object was selected as the first object due to the previousfirst object being erroneously excluded from the vehicle moving laneobject. In this case, the routine proceeds to step 204.

In step 204, it is determined whether or not the curve movement isdetected for the previous first object. Specifically, the determinationis preformed based on the condition used in steps 168 and 170 shown inFIG. 23 when the previous first object is the short distance object; thecondition used in steps 176 and 178 shown in FIG. 23 when the previousfirst object is the long distance object; and the condition used insteps 114 and 116 when the previous first object is the middle distanceobject.

If it is determined, in step 204, that the curve movement is detected onthe previous first object, it is determined that the possibility oferroneous exclusion of the previous first object is high. In this case,the routine proceeds to step 206.

In step 206, a flag FLOST is set to "1". The flag FLOST is provided forindicating that there is a high possibility of the previous first objectbeing erroneously excluded from the vehicle moving lane objects. Afterthe process of step 206 is completed, the routine proceeds to step 208.

In step 208, it is determined whether or not a predetermined time periodτ sec has passed since the flag FLOST was set to "1". If it isdetermined that the period τ sec is has not been passed yet, the routineis ended. On the other hand, if it is determined that the period τ sechas been passed, the routine proceeds to step 210.

In step 210, the flag FLOST is reset to "0", and the routine is ended.In the above-mentioned process, the value of the flag FLOST ismaintained to be "1" during the period τ sec after it is set to "1" instep 206.

If it is determined, in step 202, that the present first object is thesame as the previous first object, or if it is determined, in step 204,that the curve movement is not detected on the previous first object,the routine proceeds to step 212.

In step 212, is determined that the flag FLOST is set to "1". If it isdetermined that the flag FLOST is set to "1", the routine proceeds tostep 208. On the other hand, if it is determined that the flag FLOST isnot set to "1", the routine proceeds to step 214.

In step 214, the first object is updated to the object selected in thepresent process. According to the above-mentioned process, the updatingof the first object is permitted excluding the period τ sec after it isdetermined that there is a high possibility that the previous firstobject was erroneously excluded.

Accordingly, if it is determined that there is a high possibility thatthe previous first object is erroneously excluded from the vehiclemoving lane objects, the first object is not permitted to be updatedduring the time period τ sec after the determination was made. Thus, theerroneous selection of the first object is prevented when the previousfirst object is erroneously excluded. This means that the erroneousdetermination of the first object being selected from other objects iseliminated when the first object enters or exits a curve.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A scan-type radar apparatus provided on avehicle, the apparatus comprising:a scan-type radar for detectingobjects existing in a detectable range, said scan-type radar assuming avehicle moving lane area corresponding to a vehicle moving lane in whichsaid vehicle is moving based on an operating condition of said vehicle,said vehicle moving lane area being assumed within said detectablerange; object direction detecting means for detecting an actualdirection of said each of the objects detected by said scan-type radarwith respect to said vehicle; delay direction calculating means forcalculating a delay direction when the actual direction detected by saidobject direction detecting means is changed with respect to time, thedelay direction indicating a direction of a virtual position of each ofthe objects with respect to said vehicle by being provided with apredetermined time delay with respect to change in the actual direction;and existence determining means for determining whether said each objectexists within said vehicle moving lane by comparing the calculated delaydirection of each object with the vehicle moving lane area; wherein saiddelay direction calculating means comprises a blunted value calculatingmeans for calculating a blunted value of the actual direction as thedelay direction.
 2. The scan-type radar apparatus as claimed in claim 1,wherein said blunted value is obtained from the actual direction beingprocessed by a digital filter.
 3. The scan-type radar apparatus asclaimed in claim 1, further comprising change rate detecting means fordetecting a change rate of the actual direction of said each of theobjects, wherein said existence determining means comprises lane widthchanging means for decreasing a width of said vehicle moving lane areawhen the change rate exceeds a predetermined value.
 4. The scan-typeradar apparatus as claimed in claim 1, wherein said delay directioncalculating means comprises delay amount setting means for providing thepredetermined time delay to said each of the objects detected by saidscan-type radar.
 5. The scan-type radar apparatus as claimed in claim 1,further comprising correspondence determining means for determiningwhether the change in the actual direction of said each of the objectscorresponds to each other, wherein said existence determining meanscomprises determination maintaining means for determining that one ofthe objects continuously exists in said vehicle moving lane when a shiftin the actual direction of said one of the objects which has beendetermined to exist in said vehicle moving lane corresponds to a shiftin the direction of at least another one of the objects.
 6. Thescan-type radar apparatus as claimed in claim 5, wherein saidcorrespondence determining means comprises time difference assumingmeans for assuming a time difference between a start time of a shift inthe actual direction of the objects based on each distance between theobjects.
 7. The scan-type radar apparatus as claimed in claim 1, furthercomprising excluding means for excluding a short distance object fromthe objects determined to exist in said vehicle moving lane when a shiftin the actual direction of said short distance object has a change rategreater than a predetermined value for a predetermined time period, saidshort distance object being one of the objects positioned within apredetermined short distance from said vehicle in said vehicle movinglane.
 8. The scan-type radar apparatus as claimed in claim 1, furthercomprising recognizing means for recognizing a long distance object asan object existing in said vehicle moving lane during a firstpredetermined time period, after a change has occurred in the directionof said long distance object with a continuous change rate of more thana predetermined value for a second predetermined time period, said longdistance object being positioned beyond a predetermined long distancefrom said vehicle.